Optical storing apparatus

1. An optical storing apparatus comprising: a pickup for moving an irradiating position of a laser beam to an arbitrary track position on a medium; an information signal processing unit for reproducing at least information to said medium by said laser beam; a position signal detecting unit for detecting a position signal Y according to a positional deviation amount X in which a track center of fie medium is set to 0 on the basis of return light of said laser beam from the medium; a position signal correcting unit for outputting a corrected position signal Z obtained by correcting detection sensitivity characteristics for said positional deviation amount to desired characteristics by performing a correcting arithmetic operation using a predetermined non-linear function on the basis of said position signal Y; and a positioning control unit for performing control such that said laser beam is moved toward a target track of said medium and the laser beam is lead-n controlled to the center of the target track by switching a control mode to a position servo control at a position just before the target track and the laser beam is allowed to trace the target track after completion of the lead in control, wherein said corrected position signal Z is used for at least one of said lead-in control and said tracing of said target track.

2. An apparatus according to claim 1 , wherein said position signal correcting unit defines an ideal position signal Z desired as a desired position signal for an actual positional deviation amount X of said laser beam, executes a correcting arithmetic operation using a predetermined non-linear function to said position signal Y, and outputs the corrected position signal Z which is approximated to or coincided with said ideal position signal Z desired .

3. An apparatus according to claim 2 , wherein when an absolute value of the position signal Y detected by said position signal detecting unit is equal to or larger than a predetermined threshold value Y th , said position signal correcting unit executes a correcting arithmetic operation using a predetermined non-linear function to said position signal Y, thereby calculating the corrected position signal Z.

4. An apparatus according to claim 2 , wherein said position signal correcting unit sets an Nth order polynomial Z a N Y N a N 1 Y N 1 . . . a 2 Y 2 a 1 Y a 0 as said non-linear function and substitutes said position signal Y into said Nth order polynomial, thereby calculating the corrected position signal Z.

5. An apparatus according to claim 2 , wherein when a threshold value Y th of a positive value is set to a predetermined value which is equal to or smaller than a maximum amplitude of the position signal Y, said position signal correcting unit calculates said corrected position signal Z by Z K YZ Y in a range ( Y Y th ) where an absolute value Y of said position signal Y is equal to or smaller than the threshold value Y th , calculates the corrected position signal Z by substituting said position signal Y into an Nth order polynomial Z a N Y N a N 1 Y N 1 . . . a 2 Y 2 a 1 Y a 0 in a range (Y th <Y) where said position signal Y exceeds said threshold value Y th of a positive value, and calculates the corrected position signal Z by substituting said position signal Y into an Nth order polynomial Z (a N Y N a N 1 Y N 1 . . . a 2 Y 2 a 1 Y a 0 ) in a range (Y< Y th ) where said position signal Y is smaller than said threshold value Y th of a negative value.

6. An apparatus according to claim 4 , wherein said position signal correcting unit calculates the corrected position signal Z by substituting said position signal Y into a quadratic polynomial Z a 2 Y 2 a 1 Y a 0 in a range (Y th <Y) where said position signal Y exceeds a threshold value Y th of a positive value, and calculates the corrected position signal Z by substituting said position signal Y into a quadratic polynomial Z (a 2 Y 2 a 1 Y a 0 ) in a range (Y< Y th ) where said position signal Y is smaller than said threshold value Y th of a negative value.

7. An apparatus according to claim 2 , wherein said position signal correcting unit uses linear characteristics of Z desired K XZ X as said ideal position signal Z desired .

8. An apparatus according to claim 2 , wherein as said ideal position signal Z desired , said position signal correcting unit uses linear characteristics of Z desired K XZ X in a range ( X X th ) where an absolute value X of said positional deviation amount X lies within a threshold value X th , uses non-linear characteristics of Z desired K XZ X K NL (X X th ) n in a range (X th <X) where said positional deviation amount X exceeds said threshold value X th of a positive value, and, further, uses non-linear characteristics of Z desired K XZ X K NL ( X X th ) n in a range (X< X th ) where said positional deviation amount X is smaller than said threshold value X th of a negative value.

9. An apparatus according to claim 1 , wherein the non-linear function in said position signal correcting unit is prepared as a table and a correction is executed by referring to said table.

10. An apparatus according to claim 1 , wherein said position signal correcting unit sets an Nth order monomial equation as said non-linear function and substitutes said position signal Y into said Nth order monomial equation, thereby calculating the corrected position signal Z.

11. An apparatus according to claim 10 , wherein when a threshold value Y th is set to a value (Y max K th ) obtained by multiplying a maximum amplitude Y max of the position signal Y by a positive coefficient K th of 1 or smaller, said position signal correcting unit calculates said corrected position signal Z by Z Y in a range ( Y Y th ) where an absolute value Y of said position signal Y is equal to or smaller than the threshold value Y th , calculates the corrected position signal Z by substituting said position signal Y into an Nth order monomial equation Z Y N /Y th (N 1) in a range (Y th <Y) where said position signal Y exceeds said threshold value Y th of a positive value, and calculates the corrected position signal Z by substituting said position signal Y into an Nth order monomial equation Z Y N /Y th (N 1) in a range (Y< Y th ) where said position signal Y is smaller than said threshold value Y th of a negative value.

12. An apparatus according to claim 11 , wherein said position signal correcting unit calculates the corrected position signal Z by substituting said position signal Y into a quadratic monomial equation Z Y 2 /Y th in a range (Y th <Y) where said position signal Y exceeds said threshold value Y th of a positive value and calculates the corrected position signal Z by substituting said position signal Y into a quadratic monomial equation Z Y 2 /Y th in a range (Y< Y th ) where said position signal Y is smaller than said threshold value Y th of a negative value.

13. An apparatus according to claim 10 , wherein said position signal correcting unit calculates the corrected position signal Z by substituting said position signal Y into a cubic monomial equation Z Y 3 /Y th 2 in a range (Y th <Y) where said position signal Y exceeds a threshold value Y th of a positive value and calculates the corrected position signal Z by substituting said position signal Y into a cubic monomial equation Z Y 3 /Y th 2 in a range (Y< Y th ) where said position signal Y is smaller than said threshold value Y th of a negative value.